In digital cameras, the structure of imaging processing systems that capture a subject as an image mainly has single-chip and three-chip types. Single-chip cameras include one solid-state imaging element, and this one-chip solid-state imaging element is used to generate color signals of three primary colors RGB. For example, Japanese Unexamined Patent Application Publication No. 10-150668 describes an imaging device in which color filters that respectively allow red color, green color, and blue color to pass therethrough are arranged on a one-chip CCD image sensor in a check pattern to generate color signals R, G, and B and in which an image signal with an enhanced resolution is generated using a correlation process and an interpolation process. There is a problem in that a false color occurs in such an image signal with an enhanced resolution.
Three-chip cameras, on the other hand, include three solid-state imaging elements, and red color light, green color light, and blue color light separated by a spectroscopic mirror are individually incident on the three solid-state imaging elements. Those solid-state imaging elements independently generate color signals of red color, green color, and blue color, respectively. The three-chip cameras independently sense light of the three primary colors using the solid-state imaging elements, and yield more reproducible images with higher resolution than those of single-chip cameras. However, due to the increased circuit size and also increased amount of image processing, a longer time is required to read color signals from the solid-state imaging elements.
Further, in the three-chip cameras, there are a square pixel alignment process and a square pixel shift process as processes of generating an image signal from color signals of red color, green color, and blue color obtained from the individual solid-state imaging elements.
The square pixel alignment process is a process of, as shown in FIG. 13A, spatially matching positions of pixels in individual color signals obtained from individual solid-state imaging elements. That is, in the square pixel alignment process, the number of pixels read by a photosensitive sensor is equal to the number of pixels of an image signal on the output side. Thus, in order to increase the resolution of an image signal in this process, it needs to be increased by a magnification similar to that of the number of pixels on the photosensitive sensor side. For example, in a case where the resolution of a still image on the output side is to be increased from 3 Mpixel to 6 Mpixel, the number of pixels on the photosensitive sensor side should also be increased from 3 Mpixel to 6 Mpixel.
Further, in the square pixel shift process, as shown in FIG. 13B, pixel arrays of color signals of red color and blue color are individually shifted horizontally by d/2, which is half pixel size d, with respect to a pixel array of a color signal of green color, and the color signals of the shifted pixels are interpolated to obtain an imaging signal with an enhanced resolution. In this method, the number of pixels of an imaging signal on the output side becomes twice the number of pixels of the individual solid-state imaging elements. In other words, the number of pixels of the solid-state imaging elements is half the number of pixels of an image signal on the output side.
Here, as the resolution per frame increases, the time required to read a color signal from a solid-state imaging element increases. Furthermore, there are hardware constraints to increasing such a color signal reading speed. Therefore, in a case where an image signal with a similar resolution is to be obtained, the square pixel shift process allows an image signal having substantially the same resolution as that of the square pixel alignment process to be generated using the interpolation process even though the number of pixels of a solid-state imaging element is half, thus achieving substantially the same frame rate even if the reading speed is low.